Semiconductor device

ABSTRACT

According to one embodiment, a semiconductor device includes a semiconductor layer, an electrode, and an insulating portion. The semiconductor layer has a first surface. The electrode is provided on the first surface of the semiconductor layer. The insulating portion includes a first layer and a second layer. The first layer covers the electrode on the first surface of the semiconductor layer and has a first internal stress along the first surface. The second layer is provided on the first layer and has a second internal stress in a reverse direction of the first internal stress.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims the benefit of priorityunder 35 U.S.C. § 120 from U.S. Ser. No. 14/026,003 filed Sep. 13, 2013,and claims the benefit of priority under 35 U.S.C. § 119 from JapanesePatent Application No. 2012-224218 filed Oct. 9, 2012; the entirecontents of each of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor device.

BACKGROUND

A semiconductor device using a wide-gap semiconductor such as galliumnitride (GaN), silicon carbide (SiC), and diamond is more excellent inimportant characteristics such as breakdown voltage, electron mobility,and thermal conductivity than a semiconductor device using silicon (Si).Especially, in an HEMT (High Electron Mobility Transistor) having anAlGaN/GaN heterostructure as one form of a semiconductor device usingGaN, an excellent radio frequency characteristic and low on-resistancecan be achieved since the HEMT has high electron mobility and a highcarrier density.

In such a wide-gap semiconductor, a substrate such as a wafer is used inwhich a wide-gap semiconductor is epitaxially grown on an Si substrate,which is inexpensive and easy to have a large diameter. In a case wherea GaN-based material is to be epitaxially grown on an Si substrate, forexample, lattice mismatch between Si and the GaN-based material is asmuch as 17 to 19%. When the lattice mismatch is large, a warping amountof the substrate increases.

In a semiconductor device, it is important to control warping of thesubstrate and improve a manufacturing yield.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating the configuration of asemiconductor device according to a first embodiment;

FIG. 2A and FIG. 2B are schematic views illustrating warping;

FIG. 3 is a schematic cross-sectional view illustrating theconfiguration of a semiconductor device according to a secondembodiment;

FIG. 4 is a schematic plan view illustrating the configuration of thesemiconductor device according to the second embodiment;

FIG. 5A to FIG. 7B are schematic cross-sectional views describing amethod for manufacturing the semiconductor device; and

FIG. 8 is a schematic cross-sectional view illustrating theconfiguration of a semiconductor device according to a third embodiment.

DETAILED DESCRIPTION

According to one embodiment, a semiconductor device includes asemiconductor layer, an electrode, and an insulating portion. Thesemiconductor layer has a first surface. The electrode is provided onthe first surface of the semiconductor layer. The insulating portionincludes a first layer and a second layer. The first layer covers theelectrode on the first surface of the semiconductor layer and has afirst internal stress along the first surface. The second layer isprovided on the first layer and has a second internal stress in areverse direction of the first internal stress.

Various embodiments will be described hereinafter with reference to theaccompanying drawings. It is to be noted that, in the followingdescription, identical components in the drawings are shown with thesame reference numerals, and description of the duplicate components isomitted as needed.

First Embodiment

FIG. 1 is a schematic view illustrating the configuration of asemiconductor device according to a first embodiment.

As shown in FIG. 1, a semiconductor device 110 according to the firstembodiment includes a semiconductor layer 10, an electrode 20, and aninsulating portion 30. The semiconductor device 110 is an electronicdevice (such as a diode, a transistor, a light-emitting element, alight-receiving element, a resistor, and a capacitor) including at leastthe semiconductor layer 10 and the electrode 20.

The semiconductor layer 10 has a first surface 10 a. Examples of thesemiconductor layer 10 include not only Si but also varioussemiconductors such as a nitride semiconductor such as GaN, SiC, galliumarsenic (GaAs), indium phosphorus (InP), indium gallium phosphorus(InGaP), indium arsenide (InAs), and indium gallium arsenic (InGaAs).

The electrode 20 is provided on the first surface 10 a of thesemiconductor layer 10. In the embodiment, a direction connecting thesemiconductor layer 10 with the electrode 20 is referred to as aZ-direction, one of directions perpendicular to the Z-direction isreferred to as an X-direction, and a direction perpendicular to theZ-direction and the X-direction is referred to as a Y-direction.Further, in the embodiment, a direction in the Z-direction from thesemiconductor layer 10 toward the electrode 20 is referred to as anupward direction while an opposite direction is referred to as adownward direction.

The electrode 20 is provided to contact a part of the first surface 10a, for example. The electrode 20 may be provided via a film provided onthe first surface 10 a. The electrode 20 extends in the Y-direction, forexample. Ni is used for the electrode 20, for example.

The insulating portion 30 has a first layer 31 and a second layer 32.The first layer 31 is provided on the first surface 10 a of thesemiconductor layer 10 so as to cover the electrode 20. The first layer31 is a protective layer of the electrode 20. A thickness t31 of thefirst layer 31 is thicker than a thickness t20 of the electrode 20. Anupper surface and respective side surfaces of the electrode 20 arecovered with the first layer 31.

For the first layer 31, at least one of silicon nitride (SiN), siliconoxide (SiO₂), and silicon oxynitride (SiON) is used, for example. Thethickness t31 of the first layer 31 is approximately 0.2 micrometers(μm) or more and 0.3 μm or less, for example, although the thickness t31differs with the thickness t20 and a material of the electrode 20. Thefirst layer 31 has first internal stress along the first surface 10 a.The first internal stress is tensile stress or compressive stress, forexample.

The second layer 32 is provided on the first layer 31. The second layer32 contacts the first layer 31. For the second layer 32, at least one ofSiN, SiO₂, and SiON is used, for example. The second layer 32 has athickness t32. The second layer 32 has second internal stress in areverse direction of the first internal stress of the first layer 31. Ina case where the first internal stress is tensile stress, the secondinternal stress is compressive stress. In a case where the firstinternal stress is compressive stress, the second internal stress istensile stress. That is, the second layer 32 is a stress relaxationlayer relaxing the first internal stress contained in the first layer31.

A magnitude of force (internal force) acting in the second layer 32 isset by at least one of the thickness t32, a material, an additive, and amanufacturing method of the second layer 32, for example. That is, themagnitude of the internal force in the second layer 32 is adjusted bythe thickness t32, for example. Further, by setting a materialcomposition of the second layer 32 to be different from a materialcomposition of the first layer 31, the second internal stress in areverse direction of the first internal stress is obtained.

Further, even in a case where the material composition of the secondlayer 32 is the same as the material composition of the first layer 31,the second internal stress in a reverse direction of the first internalstress is obtained depending on a material and an amount of the additiveincluded in the second layer 32. Further, the magnitude of the secondinternal stress is adjusted by the material and the amount of theadditive included in the second layer 32.

Further, by the manufacturing method of the second layer 32 as well, thesecond internal stress in a reverse direction of the first internalstress is obtained, and the magnitude of the second internal stress isadjusted. For example, even in a case where the material of the firstlayer 31 and the material of the second layer 32 are the same, thesecond internal stress with predetermined magnitude is obtained byforming the second layer 32 in a different manufacturing method from amanufacturing method of the first layer 31. Further, even in a casewhere the manufacturing method of the first layer 31 and themanufacturing method of the second layer 32 are the same, the secondinternal stress with predetermined magnitude is obtained by forming thesecond layer 32 under different manufacturing conditions frommanufacturing conditions of the first layer 31.

The thickness t32 of the second layer 32 is thinner than the thicknesst31 of the first layer 31, for example. The thickness t32 of the secondlayer 32 is a fraction of the thickness t31 such as approximately 0.05μm, although the thickness t32 differs with a magnitude of the firstinternal stress and the material. When the thickness t32 is thinner thanthe thickness t31, a process condition for the first layer 31 has onlyto be determined mainly as a process condition for the insulatingportion 30.

The first internal stress of the first layer 31 and the second internalstress of the second layer 32 are measured by an X-ray diffractionmethod, for example. For example, a layer under measurement of internalstress is irradiated with an X-ray at a predetermined angle to derive aBragg angle θ. Lattice spacing is then derived from the Bragg angle θ,and the internal stress is derived from a difference between standardlattice spacing for the material and the derived lattice spacing,Young's modulus, and Poisson's ratio.

The first internal stress and the second internal stress may be measuredby an electron backscatter diffraction method as well. In the electronbackscatter diffraction method, a layer under measurement of internalstress is irradiated with an electron beam at a predetermined angle.Subsequently, a diffraction electron beam on a crystal plane at anapproximately 50 nm or less region below the surface irradiated with theelectron beam is obtained. By analyzing this diffraction electron beam,lattice strain is measured, and the internal stress is derived.

The first internal stress and the second internal stress may be measuredby an electron diffraction method as well. In the electron diffractionmethod, a layer under measurement of internal stress is irradiated withan electron beam at a predetermined angle. Subsequently, lattice spacingis measured from obtained diffraction spots. Lattice strain is measuredfrom changes of the measured lattice spacing from reference latticespacing to derive the internal stress.

In the semiconductor device 110, the first internal stress of the firstlayer 31 covering the electrode 20 is relaxed by the second internalstress of the second layer 32. In a case where the thickness t32 of thesecond layer 32 is thinner than the thickness t31 of the first layer 31,the second internal stress is larger than the first internal stress.Thus, warping of the semiconductor layer 10 caused by the first internalstress is suppressed. Accordingly, in a manufacturing process afterformation of the insulating portion 30, reduction in manufacturing yieldcaused by warping of the semiconductor layer 10 is suppressed. Forexample, suppression of warping of the semiconductor layer 10 suppressesexposure deviation caused by warping in a photolithography process afterformation of the insulating portion 30. Thus, high-accuracyphotolithography is performed, causing manufacturing yield to beimproved.

FIGS. 2A and 2B are schematic views illustrating warping.

FIG. 2A schematically shows a state of warping when the first layer 31is formed on the first surface 10 a of the semiconductor layer 10. FIG.2B schematically shows a state of warping when the second layer 32 isformed on the first layer 31.

As shown in FIG. 2A, when the first layer 31 is formed on the firstsurface 10 a of the semiconductor layer 10, warping is generated in thesemiconductor layer 10 due to first internal stress P10 of the firstlayer 31. In the example shown in FIG. 2A, the first internal stress P10is tensile stress in an X-direction. Due to the first internal stressP10, which is tensile stress, the electrode 20 covered with the firstlayer 31 receives stress P11, which is compressive stress. Further, inan internal portion of the semiconductor layer 10 facing the firstsurface 10 a, stress P12, which is compressive stress opposing the firstinternal stress P10, is generated. Thus, the semiconductor layer 10warps in an upward recess shape.

When the second layer 32 is formed on the first layer 31 as shown inFIG. 2B, the first internal stress P10 of the first layer 31 is relaxedby second internal stress P20 of the second layer 32. In the exampleshown in FIG. 2B, the second internal stress P20 is compressive stressin the X-direction. The first internal stress P10 is relaxed by thissecond internal stress P20, and warping of the semiconductor layer 10warping in the upward recess shape is suppressed.

For example, in a case where a transistor is manufactured by epitaxiallygrowing the semiconductor layer 10 including a GaN-based material on anSi substrate, the semiconductor layer 10 having a thickness of 3 μm ormore is normally formed on the substrate to obtain high-quality crystalsof the semiconductor layer 10 and to increase breakdown voltage in avertical direction of the substrate. When such a thick semiconductorlayer 10 is formed, the substrate warps in an upward recess shape.

In a case where a device is manufactured on a substrate having a largewarping amount as in the above case, forming a thick interlayerinsulating film between interconnects in a manufacturing procedure mayfurther increase warping of the substrate, for example. When the warpingamount of the substrate varies, reliable carriage and reliable holdingbecome difficult in a carrying system and a vacuum-chuck system of amanufacturing apparatus depending on the variation amount, which causesreduction in manufacturing yield.

In the embodiment, since variation in the warping amount during theprocess is suppressed by the insulating portion 30 to be formed on thesemiconductor layer 10, reduction in yield caused by warping issuppressed.

Meanwhile, although a case in which the first internal stress P10 istensile stress has been illustrated in the examples shown in FIGS. 2Aand 2B, the same is true of a case in which the first internal stressP10 is compressive stress. In a case where the first internal stress P10is compressive stress, the stress P11, which is tensile stress, isapplied to the electrode 20, and the stress P12, which is tensilestress, is generated in an internal portion of the semiconductor layer10 facing the first surface 10 a. Thus, the semiconductor layer 10 warpsin an upward protrusion shape. In this case, the second layer 32 havingthe second internal stress P20, which is compressive stress, is formedon the first layer 31. Consequently, warping of the semiconductor layer10 warping in the upward protrusion shape is suppressed.

When warping of the semiconductor layer 10 is suppressed in this manner,accuracy in process of the insulating portion 30 and formation of a filmto be formed on the insulating portion 30 is improved. This improvesmanufacturing yield of the semiconductor device 110.

Meanwhile, there is a case in which warping is generated in thesemiconductor layer 10 after formation of the semiconductor layer 10.Generation of warping in the semiconductor layer 10 is acceptable aslong as the warping is in an allowable range for the manufacturingapparatus. On the other hand, there is a case in which warping goes overthe allowable range for the manufacturing apparatus when the first layer31 is formed on the semiconductor layer 10 in which warping isgenerated. The second layer 32 has only to have the second internalstress P20 that keeps the warping of the semiconductor layer 10 in theallowable range for the manufacturing apparatus. Consequently, variationin the warping amount of the semiconductor layer 10 is suppressed, whichenables the process to be performed in the warping amount in theallowable range for the manufacturing apparatus.

Second Embodiment

FIG. 3 is a schematic cross-sectional view illustrating theconfiguration of a semiconductor device according to a secondembodiment.

FIG. 4 is a schematic plan view illustrating the configuration of thesemiconductor device according to the second embodiment.

As shown in FIG. 3 and FIG. 4, a semiconductor device 120 according tothe second embodiment is an FET (Field Effect Transistor), for example.

As shown in FIG. 3, the semiconductor device 120 includes thesemiconductor layer 10 provided on an upper surface 1 a is of an Sisubstrate 1, for example. The semiconductor layer 10 has aheterojunction structure of GaN and AlGaN epitaxially grown on the uppersurface 1 a of the substrate 1, for example. For example, GaN isepitaxially grown on the upper surface 1 a of the substrate 1, and AlGaNis epitaxially grown on GaN.

On the first surface 10 a of the semiconductor layer 10, a gateinsulating film 35 is provided. For the gate insulating film 35, SiN,AlN, or SiO₂ is used, for example. On the gate insulating film 35, agate electrode 21 is provided. The gate electrode 21 is provided onAlGaN of the semiconductor layer 10 via the gate insulating film 35. Atparts on the first surface 10 a of the semiconductor layer 10 providedwith no gate insulating film 35, a source electrode 22 and a drainelectrode 23 are provided. The source electrode 22 and the drainelectrode 23 are provided to contact the first surface 10 a exposed byremoving parts of the gate insulating film 35. The source electrode 22and the drain electrode 23 are in ohmic contact with AlGaN of thesemiconductor layer 10. The semiconductor device 120 is an MIS-typeGaN-based HEMT.

As shown in FIG. 4, in the semiconductor device 120, a plurality of gateelectrodes 21, source electrodes 22, and drain electrodes 23 areprovided, respectively. The plurality of gate electrodes 21, theplurality of source electrodes 22, and the plurality of drain electrodes23 are disposed spaced from each other in the X-direction and parallelto each other.

The respective source electrodes 22 and the respective drain electrodes23 are disposed alternately in the X-direction. The respective gateelectrodes 21 are disposed between the source electrodes 22 and thedrain electrodes 23 disposed alternately. That is, an electrodestructure of the semiconductor device 120 is a multifinger structure.

Each one end of the plurality of gate electrodes 21 is provided with aconnecting interconnect 210. Thereby, the plurality of gate electrodes21 is provided in a comb-like shape.

On the gate electrodes 21, the source electrodes 22, and the drainelectrodes 23 is provided the insulating portion 30 (first insulatingportion) to cover these electrodes. The insulating portion 30 has thefirst layer 31 and the second layer 32 described above. Thus, warping ofthe semiconductor layer 10 caused by the first internal stress of thefirst layer 31 is suppressed by the second internal stress of the secondlayer 32.

Each of the plurality of source electrodes 22 is connected to anextending electrode 222 via a contact 221. The extending electrode 222is provided on the insulating portion 30. The contact 221 pierces theinsulating portion 30 and connects the source electrode 22 to theextending electrode 222. The extending electrode 222 is provided tocover an area from the contact 221 to an upper side of the gateelectrode 21. The extending electrode 222 functions as a field plateelectrode to the gate electrode 21.

A plurality of extending electrodes 222 is provided. Each one end of theplurality of extending electrodes 222 is provided with a connectinginterconnect 220. Thereby, the plurality of extending electrodes 222 isprovided in a comb-like shape.

Each of the plurality of drain electrodes 23 is connected to a routingelectrode 232 via a contact 231. The routing electrode 232 is providedon the insulating portion 30. The contact 231 pierces the insulatingportion 30 and connects the drain electrode 23 to the routing electrode232.

A plurality of routing electrodes 232 are provided. Each one end of theplurality of routing electrodes 232 is provided with a connectinginterconnect 230. Thereby, the plurality of routing electrodes 232 areprovided in a comb-like shape. As viewed in a Z-direction, the pluralityof routing electrodes 232 oppose a plurality of gate electrodes 21. Theplurality of the routing electrodes 232 are provided with the pluralityof the gate electrodes 21 alternately.

Further, as viewed in the Z-direction, the plurality of routingelectrodes 232 oppose the plurality of the extending electrodes 222. Theplurality of the routing electrodes 232 are provided with the pluralityof the extending electrodes 222 alternately.

On the extending electrodes 222 and the routing electrodes 232, aninsulating portion 40 (second insulating portion) is provided to coverthese electrodes. The insulating portion 40 has a third layer 41 and afourth layer 42 which are similar to the aforementioned first layer 31and second layer 32. Internal stress of the fourth layer 42 is in areverse direction of internal stress of the third layer 41. Thereby,warping of the semiconductor layer 10 caused by the internal stress ofthe third layer 41 is suppressed by the internal stress of the fourthlayer 42.

The extending electrodes 222 are connected to a source pad 227 via acontact 226. The source pad 227 is provided on the insulating portion40. The contact 226 pierces the insulating portion 40 and connects theextending electrodes 222 to the source pad 227. An interconnect 228between the contact 226 and the source pad 227 may be provided to coveran upper side of the gate electrode 21. Thereby, the interconnect 228functions as a field plate electrode to the gate electrode 21.

The routing electrodes 232 are connected to a drain pad 237 via acontact 236. The drain pad 237 is provided on the insulating portion 40.The contact 236 pierces the insulating portion 40 and connects therouting electrodes 232 to the drain pad 237.

On the source pad 227, the interconnect 228, and the drain pad 237, aninsulating portion 50 (third insulating portion) is provided to coverthese. The insulating portion 50 has a fifth layer 51 and a sixth layer52 which are similar to the aforementioned first layer 31 and secondlayer 32. Internal stress of the sixth layer 52 is in a reversedirection of internal stress of the fifth layer 51. Thereby, warping ofthe semiconductor layer 10 caused by the internal stress of the fifthlayer 51 is suppressed by the internal stress of the sixth layer 52.

In the insulating portion 50 on the source pad 227, an opening h1 isprovided. Further, in the insulating portion 50 on the drain pad 237, anopening h2 is provided. To the source pad 227 exposed from the openingh1 is connected a not-shown bonding wire to obtain conduction betweenthe source electrodes 22 and an external circuit. To the drain pad 237exposed from the opening h2, a not-shown bonding wire is connected toobtain conduction between the drain electrodes 23 and an externalcircuit.

Further, to the connecting interconnect 210 connected to the gateelectrodes 21, a gate pad 217 is connected. To the gate pad 217, anot-shown bonding wire is connected to obtain conduction between thegate electrodes 21 and an external circuit.

In such a semiconductor device 120, the insulating portions 30, 40, and50 are provided on the semiconductor layer 10 in a plurality of layers.The respective insulating portions 30, 40, and 50 is provided withstress relaxation layers (the second layer 32, the fourth layer 42, andthe sixth layer 52). As a number of layers of the insulators increases,warping is generated in the semiconductor layer 10 more easily. Thus, byproviding the respective stress relaxation layers in the insulatingportions in the respective layers, variation in the warping amount ofthe semiconductor layer 10 is suppressed effectively. When variation inthe warping amount of the semiconductor layer 10 is suppressed,alignment accuracy and the like when multilayered insulating portionsand interconnects are formed on the semiconductor layer 10 are improved.Accordingly, manufacturing yield of the semiconductor device 120 isimproved.

Although the semiconductor device 120 shown in FIG. 3 and FIG. 4including the insulating portions 30, 40, and 50 in three layers hasbeen illustrated, the same is true of a semiconductor device includinginsulating portions in two or more layers.

Next, a method for manufacturing the semiconductor device 120 will bedescribed.

FIG. 5A to FIG. 7B are schematic cross-sectional views describing themethod for manufacturing the semiconductor device.

First, as shown in FIG. 5A, the substrate 1 is prepared. For thesubstrate 1, Si, SiC, sapphire, or GaN is used, for example. A materialfor the substrate 1 is selected based on a material for thesemiconductor layer 10 to be formed on the substrate 1, for example. Inthe embodiment, an example of using the Si substrate 1 is described.

Subsequently, the semiconductor layer 10 is formed on the upper surface1 a of the substrate 1. In the embodiment, the semiconductor layer 10includes GaN and AlGaN. For example, a buffer layer is grown on theupper surface 1 a of the substrate 1, on which GaN is epitaxially grown,on which AlGaN is epitaxially grown. For the epitaxial growth, an LPE(Liquid Phase Epitaxy) method, an HVPE (Hydride Vapor Phase Epitaxy)method, an MOCVD (Metal Organic Chemical Vapor Deposition) method, or anMBE (Molecular Beam Epitaxy) method is used, for example. A thickness ofGaN is 3 micrometers (μm), for example. A thickness of AlGaN is 30 nm,for example.

Subsequently, the gate insulating film 35 is formed on the first surface10 a of the semiconductor layer 10. The gate insulating film 35 isformed by CVD (Chemical Vapor Deposition), for example. A material forthe gate insulating film 35 includes SiN, AlN, and SiO₂, for example. Athickness of the gate insulating film 35 is 20 nm, for example.

Subsequently, as shown in FIG. 5B, parts of the gate insulating film 35are etched and removed to expose the semiconductor layer 10. At theparts from which the semiconductor layer 10 is exposed, the sourceelectrode 22 and the drain electrode 23 are formed. Further, the gateelectrode 21 is formed on the gate insulating film 35. A material forthe gate electrode 21 is Ni, for example. Materials for the sourceelectrode 22 and the drain electrode 23 are stacked Ti and Al, forexample.

The gate electrode 21, the source electrode 22, and the drain electrode23 are formed by a vacuum deposition method or a sputtering method, forexample. A thickness of the gate electrode 21 is 0.2 μm, for example, athickness of the source electrode 22 is 0.2 μm, for example, and athickness of the drain electrode 23 is 0.2 μm, for example.

Subsequently, as shown in FIG. 5C, the insulating portion is formed tocover the gate electrode 21, the source electrode 22, and the drainelectrode 23. First, the first layer is formed to cover the gateelectrode 21, the source electrode 22, and the drain electrode 23.Thereafter, the second layer 32 is formed on the first layer 31.

A material for the first layer 31 is SiN, for example. The first layer31 is formed by plasma CVD, for example. In an example of film formingconditions for the first layer 31 by the plasma CVD, SiH₄, NH₃, and N₂are used for material gas. Pressure is 80 Pascal (Pa), discharge voltageis 50 watt (W), and a film forming temperature is 375° C. A thickness ofthe first layer 31 is approximately 0.2 μm or more and 0.3 μm or less,for example. Thus, the first internal stress is contained in the firstlayer 31.

Here, in a case where the first surface 10 a of the semiconductor layer10 is a surface parallel to c plane (0001) of GaN, the first internalstress is tensile stress. When the first layer 31 containing tensilestress is formed, compressive stress is given to the gate electrode 21.When the compressive stress is given to the gate electrode 21, piezocharge is generated in the semiconductor layer 10 around an end of thegate electrode 21. Electric field concentration around the end of thegate electrode 21 is alleviated by this piezo charge, and breakdownvoltage is improved.

On the other hand, when large tensile stress is contained in the firstlayer 31, significant warping may be generated in the semiconductorlayer 10. To cope with this, the second layer 32 having the secondstress in a reverse direction of the first internal stress is formed onthe first layer 31.

A material for the second layer 32 is SiN, for example. The second layer32 is formed by a sputtering method, for example. In film formingconditions for the second layer 32 by the sputtering method, Si as atarget material is sputtered by N₂ plasma, for example. A thickness ofthe second layer 32 is approximately 0.05 μm, for example. Depending ona material, a manufacturing method, a thickness, and the like of thesecond layer 32, the second internal stress in a reverse direction ofthe first internal stress in the first layer 31 is contained in thesecond layer 32.

By providing the insulating portion 30 including the first layer 31 andthe second layer 32, warping of the semiconductor layer 10 is suppressedfurther than in a case of providing only the first layer 31.

Subsequently, as shown in FIG. 6A, a hole SH1 is formed in theinsulating portion 30 on the source electrode 22, and a hole SH2 isformed in the insulating portion 30 on the drain electrode 23. The holeSH1 pierces the second layer 32 to the first layer 31 of the insulatingportion 30 and reaches a surface of the source electrode 22. The holeSH2 pierces the second layer 32 to the first layer 31 of the insulatingportion 30 and reaches a surface of the drain electrode 23.

The holes SH1 and SH2 are formed by wet etching or dry etching. When athickness of the second layer 32 is sufficiently thinner than athickness of the first layer 31, an etching condition for the firstlayer 31 has only to be adjusted mainly as an etching condition forformation of the holes SH1 and SH2. That is, etching of the insulatingportion 30 is performed with little consideration of an etchingcondition for the second layer 32. For example, an optimal etchingcondition for the first layer 31 has only to be applied, and etchingtime has only to be extended in accordance with the thickness of thesecond layer 32.

Subsequently, the contact 221 is formed in the hole SH1, and theextending electrode 222 connected to the contact 221 and extending alongan upper surface of the insulating portion 30 is formed. Further, thecontact 231 is formed in the hole SH2, and the routing electrode 232connected to the contact 231 is formed. To form the contact 221, thecontact 231, the extending electrode 222, and the routing electrode 232,a conductive material is first formed on an entire surface of the uppersurface of the insulating portion 30. At this time, the conductivematerial buried in the hole SH1 becomes the contact 221 while theconductive material buried in the hole SH2 becomes the contact 231.Thereafter, the conductive material is patterned to form the extendingelectrode 222 and the routing electrode 232.

Subsequently, as shown in FIG. 6B, the insulating portion 40 is formedto cover the extending electrode 222 and the routing electrode 232.First, the third layer 41 is formed to cover the extending electrode 222and the routing electrode 232. Thereafter, the fourth layer 42 is formedon the third layer 41.

A material for the third layer 41 is SiO₂, for example. The third layer41 is formed by plasma CVD, for example. In an example of film formingconditions for the third layer 41 by the plasma CVD, SiH₄, N₂O, and N₂are used for material gas. Pressure is 80 Pa, discharge voltage is 50 W,and a film forming temperature is 350° C. A thickness of the third layer41 is approximately 0.2 μm or more and 0.8 μm or less, for example.Thus, third internal stress is contained in the third layer 41.

A material for the fourth layer 42 is SiN, for example. The fourth layer42 is formed by a sputtering method, for example. In film formingconditions for the fourth layer 42 by the sputtering method, Si as atarget material is sputtered by N₂ plasma, for example. A thickness ofthe fourth layer 42 is approximately 0.05 μm, for example. Depending ona material, a manufacturing method, a thickness, and the like of thefourth layer 42, fourth internal stress in a reverse direction of thethird internal stress in the third layer 41 is contained in the fourthlayer 42.

By providing the insulating portion 40 including the third layer 41 andthe fourth layer 42, warping of the semiconductor layer 10 is suppressedfurther than in a case of providing only the third layer 41.

Subsequently, as shown in FIG. 7A, a hole SH3 is formed in theinsulating portion 40 on the extending electrode 222, and a hole SH4 isformed in the insulating portion 40 on the routing electrode 232. Thehole SH3 pierces the fourth layer 42 to the third layer 41 of theinsulating portion 40 and reaches a surface of the extending electrode222. The hole SH4 pierces the fourth layer 42 to the third layer 41 ofthe insulating portion 40 and reaches a surface of the routing electrode232.

When a thickness of the fourth layer 42 is sufficiently thinner than athickness of the third layer 41, an etching condition for the thirdlayer 41 has only to be adjusted mainly in formation of the holes SH3and SH4.

Subsequently, the contact 226 is formed in the hole SH3, and theinterconnect 228 and the source pad 227 connected to the contact 226 andextending along an upper surface of the insulating portion 40 is formed.Further, the contact 236 is formed in the hole SH4, and the drain pad237 connected to the contact 236 is formed. To form the contact 226, thecontact 236, the interconnect 228, the source pad 227, and the drain pad237, a conductive material is first formed on an entire surface of theupper surface of the insulating portion 40. At this time, the conductivematerial buried in the hole SH3 becomes the contact 226 while theconductive material buried in the hole SH4 becomes the contact 236.Thereafter, the conductive material is patterned to form theinterconnect 228, the source pad 227, and the drain pad 237.

Subsequently, as shown in FIG. 7B, the insulating portion 50 is formedto cover the interconnect 228, the source pad 227, and the drain pad237. First, the fifth layer 51 is formed to cover the interconnect 228,the source pad 227, and the drain pad 237. Thereafter, the sixth layer52 is formed on the fifth layer 51.

A material for the fifth layer 51 is SiN, for example. The fifth layer51 is formed by plasma CVD, for example. In an example of film formingconditions for the fifth layer 51 by the plasma CVD, SiH₄, NH₃, and N₂are used for material gas. Pressure is 80 Pa, discharge voltage is 50 W,and a film forming temperature is 375° C. A thickness of the fifth layer51 is approximately 0.1 μm or more and 0.3 μm or less, for example.Thus, fifth internal stress is contained in the fifth layer 51.

A material for the sixth layer 52 is SiN, for example. The sixth layer52 is formed by a sputtering method, for example. In film formingconditions for the sixth layer 52 by the sputtering method, Si as atarget material is sputtered by N₂ plasma, for example. A thickness ofthe sixth layer 52 is approximately 0.05 μm, for example. Depending on amaterial, a manufacturing method, a thickness, and the like of the sixthlayer 52, sixth internal stress in a reverse direction of the fifthinternal stress in the fifth layer 51 is contained in the sixth layer52.

By providing the insulating portion 50 including the fifth layer 51 andthe sixth layer 52, warping of the semiconductor layer 10 is suppressedfurther than in a case of providing only the fifth layer 51.

Subsequently, the opening h1 is formed in the insulating portion 50 onthe source pad 227, and the opening h2 is formed in the insulatingportion 50 on the drain pad 237. Thus, the source pad 227 is exposedfrom the opening h1 while the drain pad 237 is exposed from the openingh2.

When a thickness of the sixth layer 52 is sufficiently thinner than athickness of the fifth layer 51, an etching condition for the fifthlayer 51 has only to be adjusted mainly for formation of the openings h1and h2. Consequently, the semiconductor device 120 is completed.

In such a method for manufacturing the semiconductor device 120, theinsulating portions 30, 40, and 50 provided on the semiconductor layer10 in a plurality of layers are provided with stress relaxation layers(the second layer 32, the fourth layer 42, and the sixth layer 52).Thus, variation in the warping amount of the semiconductor layer 10 issuppressed more effectively than in a case of providing no stressrelaxation layers. When variation in the warping amount of thesemiconductor layer 10 is suppressed, alignment accuracy and the likewhen multilayered insulating portions and interconnects are formed onthe semiconductor layer 10 are improved. Accordingly, manufacturingyield of the semiconductor device 120 is improved.

Third Embodiment

FIG. 8 is a schematic cross-sectional view illustrating theconfiguration of a semiconductor device according to a third embodiment.

As shown in FIG. 8, a semiconductor device 130 according to the thirdembodiment differs from the semiconductor device 120 according to thesecond embodiment in terms of manufacturing methods of a second layer320, a fourth layer 420, and a sixth layer 520. That is, the secondlayer 320, the fourth layer 420, and the sixth layer 520 of thesemiconductor device 130 are formed in different manufacturing methodsfrom those of the second layer 32, the fourth layer 42, and the sixthlayer 52 of the semiconductor device 120.

The second layer 320 of the insulating portion 30 is a layer formed inthe same manufacturing method as that of the first layer 31 of theinsulating portion 30 and under different manufacturing conditions fromthose of the first layer 31 of the insulating portion 30. The fourthlayer 420 of the insulating portion 40 is a layer formed in the samemanufacturing method as that of the third layer 41 of the insulatingportion 40 and under different manufacturing conditions from those ofthe third layer 41 of the insulating portion 40. The sixth layer 520 ofthe insulating portion 50 is a layer formed in the same manufacturingmethod as that of the fifth layer 51 of the insulating portion 50 andunder different manufacturing conditions from those of the fifth layer51 of the insulating portion 50.

For example, the first layer 31 of the insulating portion 30 is formedby plasma CVD. The second layer 320 of the insulating portion 30 isformed by continuous film forming from the first layer 31. In the middleof this continuous film forming, manufacturing conditions are changed.Thus, the second layer 320 is formed. Accordingly, there exists from thefirst layer 31 to the second layer 320 a region R in which parametersare gradually changed due to changes in manufacturing conditions such asa composition, a material for an additive, and an amount of theadditive.

To form the first layer 31 to the second layer 320, a flow rate, a flowratio, pressure, a temperature, radio frequency output, and the like ofmaterial gas for the plasma CVD are changed. Thus, the first layer 31via the region R to the second layer 320 are formed.

The fourth layer 420 of the insulating portion 40 and the sixth layer520 of the insulating portion 50 are similar to the second layer 320.That is, the fourth layer 420 is formed by continuous film forming fromthe third layer 41. By changing manufacturing conditions at this time,the third layer 41 via the region R to the fourth layer 420 are formed.The sixth layer 520 is formed by continuous film forming from the fifthlayer 51. By changing manufacturing conditions at this time, the fifthlayer 51 via the region R to the sixth layer 520 are formed.

In such a semiconductor device 130, similar effects to those of thesemiconductor device 120 can be obtained, and additionally, theinsulating portions 30, 40, and 50 can be manufactured easily.

As described above, with the embodiment, a semiconductor device in whichwarping of a substrate is suppressed can be provided.

Meanwhile, in the specification, the “nitride semiconductor” shallinclude semiconductors with all kinds of compositions having a chemicalformula of B_(x)In_(y)Al_(z)Ga_(1-x-y-z)N (0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z≤1)where composition ratios x, y, and z are changed in respective ranges.Further, the “nitride semiconductor” shall include ones having the abovechemical formula further containing a Group V element other than N(nitrogen), further containing various elements to be added to controlvarious physical properties such as a conductivity type, and furthercontaining various elements to be contained unintentionally.

The embodiments have been described above with reference to the specificexamples. However, the embodiments are not limited to these specificexamples. That is, a person skilled in the art appropriately adds designchanges to these specific examples, and such changes are encompassedwithin the scope of the embodiments as long as they have features of theembodiments. Each component included in each of the aforementionedspecific examples, and arrangement, a material, a condition, a shape, asize, and the like of the component are not limited to the illustratedones but can be changed appropriately.

Each element included in embodiments described above can be combined tothe extent possible and these combinations are also encompassed withinthe scope of the embodiments as long as they include the features of theembodiments. Various other variations and modifications can be conceivedby those skilled in the art within the spirit of the invention, and itis understood that such variations and modifications are alsoencompassed within the scope of the embodiment.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A semiconductor device comprising: a siliconsubstrate; a semiconductor layer provided on the silicon substrate, thesemiconductor layer having a first surface and including a nitridesemiconductor; a first electrode provided on the first surface of thesemiconductor layer; a second electrode provided spaced from the firstelectrode on the first surface of the semiconductor layer; a controlelectrode provided between the first electrode and the second electrodeon the first surface of the semiconductor layer; and a first insulatingportion including a first layer and a second layer, the first layercovering the control electrode on the first surface of the semiconductorlayer and having a first internal stress, the first internal stresshaving a first direction along the first surface, the second layerprovided on the first layer and having a second internal stress, thesecond internal stress having a second direction along the first surfaceand being reverse to the first direction, wherein the first internalstress is a tensile stress, the second internal stress is a compressivestress, and wherein the first surface of the semiconductor layer is asurface parallel to c plane (0001) of GaN.
 2. The device according toclaim 1, wherein a thickness of the second layer is thinner than athickness of the first layer, and the second internal stress is largerthan the first internal stress.
 3. The device according to claim 1,wherein a material composition of the second layer is different from amaterial composition of the first layer.
 4. The device according toclaim 1, wherein a material of the second layer is same as a material ofthe first layer.
 5. The device according to claim 1, further comprisinga control insulating film provided between the control electrode and thefirst surface, a material of the second layer being same as a materialof the control insulating film.
 6. The device according to claim 1,further comprising: a first extending electrode extending on the secondlayer and an extending end of the first extending electrode covering thecontrol electrode; and a contact portion connecting the first extendingelectrode to the first electrode.
 7. The device according to claim 6,further comprising a second insulating portion including a third layerand a fourth layer, the third layer covering the first extendingelectrode on the second layer and having a third internal stress alongthe first surface, the fourth layer provided on the third layer andhaving a fourth internal stress in a reverse direction of the thirdinternal stress.
 8. The device according to claim 7, wherein a thicknessof the fourth layer is thinner than a thickness of the third layer. 9.The device according to claim 7, wherein a material composition of thefourth layer is different from a material composition of the thirdlayer.
 10. The device according to claim 7, wherein a material of thefourth layer is same as a material of the third layer.